438 Mr. C. Iledley on the Range ofPlacostylus. 



and Fiji a line of soundings lias been recorded of over 2000 

 fathoms, wliile between New Caledonia and the New Hebrides 

 two soundings of 2G50 and of 2525 fathoms would indicate 

 that a gulf running south-east from the Coral Sea here inter- 

 venes. 1 he ditlVrcnecs betweeu the northern and southern 

 types of Placostylus are supplemented by other features of 

 their respective mollusk faunas. The northern type is every- 

 where accompanied by Trochomorpha^ which is never asso- 

 ciated with the southern. Species of the so-called Melanopsis 

 occur in New Zealand and in New Caledonia, but are 

 unknown in the northern archijudagoes. These scanty data 

 appear to show that early in the history of the existing fauna 

 the ^lelanesian Plateau was rent in twain and has never 

 since been united. 



The forms of Placostyhs inhabiting the Fijis resemble in 

 shape and colour sundry of the Solomon-Island species. 

 Thus elobalus from Lcvuka and christovaIen<iis from San 

 Christoval are much alike both in shape and colour-pattern, 

 and Secinanni hv\n Kandavu finds a close parallel in Mac- 

 farlandi from the Solomons. The remainder of the land- 

 mollusca of each archi[ielago contribute further evidence of 

 aflBnity ; thus Nanina nitidissima from the Solomons resembles 

 ]Sl. cosca from Fiji ; both areas also possess a Pupina. Such 

 affinity would warrant the deduction that the Solomons were 

 the source of the Fijian molluscan fauna, though the former 

 group had probably not then received from Papua the newer 

 genera of Cltloniis and Papuina. Eastwards from the 

 Melanesian Plateau Placostylus w-as unable to extend its 

 range ; but its derivative and representative Partulaj 

 together with other ]\Jelanesian emigrants, Endodonta, Torna- 

 tellina^ llelicinaj and similar minute forms, drifting east- 

 wards from island to island, colonized the oceanic groups of 

 the south-cast Pacific. 



Summary. — I would remark, firstly, on the essential unity 

 of the Placosiyhis area as a zoological ])rovince, embracing 

 the archipelagoes of Solomon, Fiji, New Hebrides, Loyalty, 

 New Caledonia, Norfolk Island (?), Lord Howe, and New 

 Zealand — a unity explicable only on the theory that they 

 fo:m portions of a shattered continent and arc connected by 

 shallow banks, formerly dry land. This continental area I 

 propose to call the Jilelanesian Plateau. Secondly, that this 

 Melanesian Plateau was never connected with nor populated 

 from Australia; probably its fauna was derived from l^apua, 

 via New Britain. The presence of genera common to 

 Australia and New Zealand is exjdicablc on the ground that 

 they mi^'-ated, not from the one territory to the other, but 



